U.S. patent number 9,776,302 [Application Number 13/983,012] was granted by the patent office on 2017-10-03 for coated abrasive article having rotationally aligned formed ceramic abrasive particles and method of making.
This patent grant is currently assigned to 3M Innovative Properties Company. The grantee listed for this patent is Steven J. Keipert. Invention is credited to Steven J. Keipert.
United States Patent |
9,776,302 |
Keipert |
October 3, 2017 |
Coated abrasive article having rotationally aligned formed ceramic
abrasive particles and method of making
Abstract
A coated abrasive article having a plurality of formed ceramic
abrasive particles each having a surface feature. The plurality of
formed ceramic abrasive particles attached to a flexible backing by
a make coat comprising a resinous adhesive forming an abrasive
layer. The surface feature having a specified z-direction
rotational orientation, and the specified z-direction rotational
orientation occurs more frequently in the abrasive layer than would
occur by a random z-direction rotational orientation of the surface
feature.
Inventors: |
Keipert; Steven J. (Somerset,
WI) |
Applicant: |
Name |
City |
State |
Country |
Type |
Keipert; Steven J. |
Somerset |
WI |
US |
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Assignee: |
3M Innovative Properties
Company (St. Paul, MN)
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Family
ID: |
46673085 |
Appl.
No.: |
13/983,012 |
Filed: |
February 1, 2012 |
PCT
Filed: |
February 01, 2012 |
PCT No.: |
PCT/US2012/023477 |
371(c)(1),(2),(4) Date: |
September 05, 2013 |
PCT
Pub. No.: |
WO2012/112305 |
PCT
Pub. Date: |
August 23, 2012 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20130344786 A1 |
Dec 26, 2013 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61443418 |
Feb 16, 2011 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B24D
3/004 (20130101); C09K 3/1409 (20130101); B24D
3/28 (20130101); B24D 2203/00 (20130101) |
Current International
Class: |
B24D
3/00 (20060101); C09K 3/14 (20060101); B24D
3/28 (20060101) |
Field of
Search: |
;51/295,298,20
;451/529,539,526 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2 085 622 |
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Jul 1993 |
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CA |
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1623731 |
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Jun 2005 |
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CN |
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2015/16579 |
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Jun 2010 |
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CN |
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1459847 |
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Sep 2004 |
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EP |
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1 995 020 |
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Nov 2008 |
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EP |
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94/07809 |
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Apr 1994 |
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WO |
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2007/146608 |
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Dec 2007 |
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WO |
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2011-068714 |
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Jun 2011 |
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WO |
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2011-087649 |
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Jul 2011 |
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WO |
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2011-139562 |
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Nov 2011 |
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WO |
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2012-018903 |
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Feb 2012 |
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WO |
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2012-112322 |
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Aug 2012 |
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WO |
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Other References
International Search Report for PCT International Application No.
PCT/US2012/023477, dated Aug. 24, 2012, 4 pages. cited by
applicant.
|
Primary Examiner: Carter; Monica
Assistant Examiner: Beronja; Lauren
Attorney, Agent or Firm: Baum; Scott A.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a national stage filing under 35 U.S.C.
.sctn.371 of PCT/US2012/023477, filed Feb. 1, 2012, which claims
priority to U.S. Provisional Patent Application No. 61/443418,
filed Feb. 16, 2011, the disclosures of which are incorporated by
reference in their entirety herein.
Claims
What is claimed is:
1. A coated abrasive article comprising: a plurality of monolithic
formed ceramic abrasive particles each having a surface feature;
the plurality of monolithic formed ceramic abrasive particles
attached to a flexible backing by a make coat comprising a resinous
adhesive forming an abrasive layer; wherein as attached to the
flexible backing, each of the monolithic formed ceramic abrasive
particles has a z-direction rotational orientation of the
corresponding surface feature about a z-axis passing through each
of the monolithic formed ceramic abrasive particles and through the
flexible backing at a substantially 90 degree angle with respect to
the backing; and further wherein the z-direction rotational
orientation of at least 50 percent of the monolithic formed ceramic
abrasive particles attached to the flexible backing is a
predetermined specified z-direction rotational orientation that is
not random and occurs more frequently in the abrasive layer than
would occur by a random z-direction rotational orientation of the
surface feature and the specified z-direction rotational
orientation of the at least 50 percent of the monolithic formed
ceramic abrasive particles is at an angle ranging from
approximately zero degrees to approximately 90 degrees relative to
a longitudinal axis of the article.
2. The coated abrasive article of claim 1 comprising a size coat
applied over the plurality of monolithic formed abrasive particles
attached to the backing.
3. The coated abrasive article of claim 1 wherein the surface
feature comprises a substantially planar surface.
4. The coated abrasive article of claim 3 wherein the coated
abrasive article comprises a disc and the specified z-direction
rotational orientation positions the substantially planar surface
circumferentially and a pattern created by the plurality of
monolithic formed ceramic abrasive particles comprises a plurality
of concentric circles.
5. The coated abrasive article of claim 3 wherein the coated
abrasive article comprises a sheet or a belt and the specified
z-direction rotational orientation positions the substantially
planar surface at an angle of approximately 0 degrees to a
longitudinal axis of the belt or the sheet and a pattern created by
the plurality of monolithic formed ceramic abrasive particles
comprises a plurality of parallel lines.
6. The coated abrasive article of claim 3 wherein the coated
abrasive article comprises a disc and the specified z-direction
rotational orientation positions the substantially planar surface
radically and a pattern created by the plurality of monolithic
formed ceramic abrasive particles comprises a plurality of
concentric circles.
7. The coated abrasive article of claim 3 wherein the coated
abrasive article comprises a sheet or a belt and the specified
z-direction rotational orientation positions the substantially
planar surface at an angle of approximately 90 degrees to a
longitudinal axis of the belt or the sheet and a pattern created by
the plurality of monolithic formed ceramic abrasive particles
comprises a plurality of parallel lines.
8. The coated abrasive article of claim 3 wherein the coated
abrasive article comprises a disc and the specified z-direction
rotational orientation positions the substantially planar surface
at an angle of approximately 45 degrees to the diameter of the disc
and a pattern created by the plurality of monolithic formed ceramic
abrasive particles comprises a plurality of parallel lines.
9. The coated abrasive article of claim 3 wherein the coated
abrasive article comprises a sheet or a belt and the specified
z-direction rotational orientation positions the substantially
planar surface at an angle of approximately 45 degrees to a
longitudinal axis of the belt or the sheet and a pattern created by
the plurality of monolithic ceramic abrasive particles comprises a
plurality of parallel lines.
10. The coated abrasive article of claim 3 wherein the coated
abrasive article comprises a disc and the specified z-direction
rotational orientation positions approximately 50% of the formed
abrasive particles having the substantially planar surface aligned
at approximately 0 degrees and approximately 50% of the formed
abrasive particles having the substantially planar surface aligned
at an angle of approximately 90 degrees and a pattern created by
the plurality of monolithic ceramic abrasive particles comprises a
plurality of orthogonal lines.
11. The coated abrasive article of claim 3 wherein the coated
abrasive article comprises a sheet or a belt and the specified
z-direction rotational orientation positions approximately 50% of
the formed abrasive particles having the substantially planar
surface aligned at approximately 0 degrees to a longitudinal axis
and approximately 50% of the formed abrasive particles having the
substantially planar surface aligned at an angle of approximately
90 degrees to the longitudinal axis and a pattern created by the
plurality of monolithic ceramic abrasive particles comprises a
plurality of orthogonal lines.
12. The coated abrasive article of claim 1 wherein at least 80% of
the monolithic formed ceramic abrasive particles have the specified
z-direction rotational orientation.
13. The coated abrasive article of claim 1 wherein the monolithic
formed ceramic abrasive particles comprise plates having two
opposed substantially planar surfaces.
14. The coated abrasive article of claim 13 wherein the opposed
substantially planar surfaces each have a triangular perimeter.
15. The coated abrasive article of claim 1 wherein the surface
feature is selected from the group consisting of a concave surface;
a convex surface; a vertex; an aperture; a ridge; a line or a
plurality of lines; a protrusion; or a depression.
16. The coated abrasive article of claim 1, wherein the z-direction
rotational orientation of less than 100 percent of the monolithic
formed abrasive particles attached to the flexible backing is the
specified z-direction rotational orientation.
Description
BACKGROUND
Abrasive particles and abrasive articles made from the abrasive
particles are useful for abrading, finishing, or grinding a wide
variety of materials and surfaces in the manufacturing of goods. As
such, there continues to be a need for improving the cost,
performance, or life of the abrasive particle and/or the abrasive
article.
Triangular shaped abrasive particles and abrasive articles using
the triangular shaped abrasive particles are disclosed in U.S. Pat.
No. 5,201,916 to Berg; U.S. Pat. No. 5,366,523 to Rowenhorst; and
U.S. Pat. No. 5,984,988 to Berg. In one embodiment, the abrasive
particles' shape comprised an equilateral triangle. Triangular
shaped abrasive particles are useful in manufacturing abrasive
articles having enhanced cut rates.
SUMMARY
Shaped abrasive particles, in general, can have superior
performance over randomly crushed abrasive particles. By
controlling the shape of the abrasive particle it is possible to
control the resulting performance of the abrasive article. The
inventors have discovered that by further controlling the shaped
abrasive particles' z-direction rotational orientation, the cut and
finish of the resulting coated abrasive article can be altered.
Coated abrasive articles are conventionally made by electrostatic
coating (e-coat) the abrasive particles onto a make layer on a
backing or drop coating the abrasive particles onto the make layer.
Controlling the z-direction rotational orientation of abrasive
particles in a coated abrasive article is not possible using
conventional electrostatic deposition methods to propel the
abrasive grain vertically against the force of gravity onto a make
layer by use of an electrostatic field thereby erectly applying the
abrasive particles as shown in U.S. Pat. No. 2,370,636. The adhered
abrasive particles to the make layer will have a random z-direction
rotational orientation since the particle's rotation as it is being
removed from the conveyor belt by the electrostatic field is random
and uncontrolled. Similarly, in drop coated abrasive articles, the
particle's z-direction rotational orientation is random as the
particles are fed from the hopper and fall by the force of gravity
onto the make layer.
During the manufacture of rigid abrasive tools, employing a metal
bond and diamond abrasive particles, screens can be used to apply
the diamond abrasive particles to a rigid support, such a metal
disc, in a particular pattern or gird. However, the diamonds in
general are not orientated to have any specific z-direction
rotational orientation and the screen apertures are such that the
diamond is free to rotate in any direction when being placed into
the screen aperture. Sometimes the diamonds are oriented with
respect to their internal crystallographic direction of maximum
hardness as discussed in U.S. Pat. No. 5,453,106; but it has been
heretofore unappreciated to rotationally align formed ceramic
abrasive particles with regard to a surface feature of the particle
to either increase the cut or alter the resulting finish.
The inventors have discovered that the use of precision screens
having precisely spaced and aligned non-circular apertures to hold
an individual abrasive particle in a fixed position can be used to
rotationally align a surface feature of the abrasive particles in a
specific z-direction rotational orientation. Alignment of the
surface feature can be used to enhance the cutting action of that
surface feature or to change the finish produced on the workpiece
by the surface feature.
Furthermore, the precision screens can be used to control the
density of the abrasive particles without requiring any specific
rotational orientation by creating a predetermined pattern with the
abrasive particles in the abrasive layer. These patterns can
achieve significantly more "vertex up" placement of the triangular
formed abrasive particles on the coated backing than electrostatic
coating methods can achieve; especially, at higher densities of the
formed abrasive particles on the coated backing.
Additionally, an engineered abrasive layer having a predetermined
pattern can be constructed where the spacing in the x and y
directions along with the z-direction rotational orientation of the
abrasive particles about a z-axis passing through the backing and
the abrasive particle is controlled.
Hence, in one embodiment, the invention resides in a coated
abrasive article comprising: a plurality of formed ceramic abrasive
particles each having a surface feature; the plurality of formed
ceramic abrasive particles attached to a flexible backing by a make
coat comprising a resinous adhesive forming an abrasive layer; the
surface feature having a specified z-direction rotational
orientation; and wherein the specified z-direction rotational
orientation occurs more frequently in the abrasive layer than would
occur by a random z-direction rotational orientation of the surface
feature.
BRIEF DESCRIPTION OF THE DRAWING
It is to be understood by one of ordinary skill in the art that the
present discussion is a description of exemplary embodiments only,
and is not intended as limiting the broader aspects of the present
disclosure, which broader aspects are embodied in the exemplary
construction.
FIGS. 1A and 1B illustrate a top view and a side view of one
embodiment of a shaped abrasive particle.
FIG. 1C illustrates a side view of a coated abrasive article.
FIGS. 2A and 2B are top views of one embodiment of coated abrasive
articles having z-direction rotationally aligned shaped abrasive
particles of FIGS. 1A and 1B.
FIG. 2C is a top view of a portion of a screen having a plurality
of rotationally aligned apertures used to make the coated abrasive
article of FIG. 2A.
FIGS. 3A and 3B are top views of another embodiment of coated
abrasive articles having z-direction rotationally aligned shaped
abrasive particles of FIGS. 1A and 1B.
FIG. 3C is a top view of a portion of a screen having a plurality
of rotationally aligned apertures used to make the coated abrasive
articles of FIG. 3A.
FIGS. 4A and 4B are top views of another embodiment of coated
abrasive articles having z-direction rotationally aligned shaped
abrasive particles of FIGS. 1A and 1B.
FIG. 4C is a top view of a portion of a screen having a plurality
of rotationally aligned apertures used to make the coated abrasive
articles of FIG. 4A.
FIGS. 5A and 5B are top views of another embodiment of coated
abrasive articles having z-direction rotationally aligned shaped
abrasive particles of FIGS. 1A and 1B.
FIG. 5C is a top view of a portion of a screen having a plurality
of rotationally aligned apertures used to make the coated abrasive
articles of FIG. 5A.
FIGS. 6 and 7 are graphs of the grinding performance of various
Examples of the invention.
FIG. 8 is a graph of cut versus percent of closed coat density for
two different methods of forming a coated abrasive article.
Repeated use of reference characters in the specification and
drawings is intended to represent the same or analogous features or
elements of the disclosure.
DEFINITIONS
As used herein, forms of the words "comprise", "have", and
"include" are legally equivalent and open-ended. Therefore,
additional non-recited elements, functions, steps or limitations
may be present in addition to the recited elements, functions,
steps, or limitations.
As used herein, the term "abrasive dispersion" means an alpha
alumina precursor that can be converted into alpha alumina that is
introduced into a mold cavity. The composition is referred to as an
abrasive dispersion until sufficient volatile components are
removed to bring solidification of the abrasive dispersion.
As used herein "formed ceramic abrasive particle" means a ceramic
abrasive particle having at least a partially replicated shape.
Non-limiting processes to make formed abrasive particles include
shaping the precursor abrasive particle in a mold having a
predetermined shape, extruding the precursor abrasive particle
through an orifice having a predetermined shape, printing the
precursor abrasive particle though an opening in a printing screen
having a predetermined shape, or embossing the precursor abrasive
particle into a predetermined shape or pattern. Non-limiting
examples of formed ceramic abrasive particles include shaped
abrasive particles formed in a mold, such as triangular plates as
disclosed in U.S. Pat. Nos. RE 35,570; 5,201,916, and 5,984,998; or
extruded elongated ceramic rods/filaments often having a circular
cross section produced by Saint-Gobain Abrasives an example of
which is disclosed in U.S. Pat. No. 5,372,620. Formed abrasive
particle as used herein excludes randomly sized abrasive particles
obtained by a mechanical crushing operation.
As used herein, the term "precursor shaped abrasive particle" means
the unsintered particle produced by removing a sufficient amount of
the volatile component from the abrasive dispersion, when it is in
the mold cavity, to form a solidified body that can be removed from
the mold cavity and substantially retain its molded shape in
subsequent processing operations.
As used herein, the term "shaped abrasive particle", means a
ceramic abrasive particle with at least a portion of the abrasive
particle having a predetermined shape that is replicated from a
mold cavity used to form the shaped precursor abrasive particle.
Except in the case of abrasive shards (e.g. as described in U.S.
patent publication US 2009/0169816, the shaped abrasive particle
will generally have a predetermined geometric shape that
substantially replicates the mold cavity that was used to form the
shaped abrasive particle. Shaped abrasive particle as used herein
excludes randomly sized abrasive particles obtained by a mechanical
crushing operation.
As used herein, "z-direction rotational orientation" refers to the
particle's angular rotation about a z-axis passing through the
particle and through the backing at a 90 degree angle to the
backing when the particle is attached to the backing by a make
layer.
DETAILED DESCRIPTION
Shaped Abrasive Particle with a Sloping Sidewall
Referring to FIGS. 1A, 1B, and 1C an exemplary shaped abrasive
particle 20 with a sloping sidewall 22 is illustrated. The material
from which the shaped abrasive particle 20 with a sloping sidewall
22 is made comprises a ceramic and specifically in one embodiment
alpha alumina. Alpha alumina particles can be made from a
dispersion of aluminum oxide monohydrate that is gelled, molded to
shape, dried to retain the shape, calcined, and then sintered. The
shaped abrasive particle's shape is retained without the need for a
binder to form an agglomerate comprising abrasive particles in a
binder that are then formed into a shaped structure.
In general, the shaped abrasive particles 20 with a sloping
sidewall 22 comprise thin bodies having a first face 24, and a
second face 26 and having a thickness t. The first face 24 and the
second face 26 are connected to each other by at least one sloping
sidewall 22. In some embodiments, more than one sloping sidewall 22
can be present and the slope or angle for each sloping sidewall 22
may be the same as shown in FIG. 1A or different.
In some embodiments, the first face 24 is substantially planar, the
second face 26 is substantially planar, or both faces are
substantially planar. Alternatively, the faces could be concave or
convex as discussed in more detail in U.S. patent publication
2010/0151195 entitled "Dish-Shaped Abrasive Particles With A
Recessed Surface", filed on Dec. 17, 2008. Additionally, an opening
or aperture through the faces could be present as discussed in more
detail in U.S. patent publication 2010/0151201 entitled "Shaped
Abrasive Particles With An Opening, filed on Dec. 17, 2008.
In one embodiment, the first face 24 and the second face 26 are
substantially parallel to each other. In other embodiments, the
first face 24 and second face 26 can be nonparallel such that one
face is sloped with respect to the other face and imaginary lines
tangent to each face would intersect at a point. The sloping
sidewall 22 of the shaped abrasive particle 20 with a sloping
sidewall 22 can vary and it generally forms the perimeter 29 of the
first face 24 and the second face 26. In one embodiment, the
perimeter 29 of the first face 24 and second face 26 is selected to
be a geometric shape, and the first face 24 and the second face 26
are selected to have the same geometric shape, although, they
differ in size with one face being larger than the other face. In
one embodiment, the perimeter 29 of first face 24 and the perimeter
29 of the second face 26 was a triangular shape that is
illustrated.
Referring to FIGS. 1B and 1C, a draft angle .alpha. between the
second face 26 and the sloping sidewall 22 of the shaped abrasive
particle 20 can be varied to change the relative sizes of each
face. In various embodiments of the invention, the draft angle
.alpha. can be between about 90 degrees to about 130 degrees, or
between about 95 degrees to about 130 degrees, or between about 95
degrees to about 125 degrees, or between about 95 degrees to about
120 degrees, or between about 95 degrees to about 115 degrees, or
between about 95 degrees to about 110 degrees, or between about 95
degrees to about 105 degrees, or between about 95 degrees to about
100 degrees. As discussed in U.S. patent publication 2010/0151196
entitled "Shaped Abrasive Particles With A Sloping Sidewall" filed
on Dec. 17, 2008, specific ranges for the draft angle .alpha. have
been found to produce surprising increases in the grinding
performance of coated abrasive articles made from the shaped
abrasive particles with a sloping sidewall.
Referring now to FIG. 1C, a coated abrasive article 40 is shown
having a first major surface 41 of a backing 42 covered by an
abrasive layer. The abrasive layer comprises a make coat 44, and a
plurality of shaped abrasive particles 20 with a sloping sidewall
22 attached to the backing 42 by the make coat 44. A size coat 46
is applied to further attach or adhere the shaped abrasive
particles 20 with a sloping sidewall 22 to the backing 42.
As seen, the majority of the shaped abrasive particles 20 with a
sloping sidewall 22 are tipped or leaning to one side. This results
in the majority of the shaped abrasive particles 20 with a sloping
sidewall 22 having an orientation angle .beta. less than 90 degrees
relative to the first major surface 41 of the backing 42. As seen,
once the shaped abrasive particles with a sloping sidewall are
applied and allowed to lean onto the sloping sidewall, the very
tips 48 of the shaped abrasive particles have generally the same
height, h.
To further optimize the leaning orientation, the shaped abrasive
particles with a sloping sidewall can be applied to the backing in
an open coat abrasive layer. A closed coat abrasive layer in an
electrostatic application system is the maximum weight of abrasive
particles or a blend of abrasive particles that can be applied to a
make coat of an abrasive article in a single pass through the
maker. An open coat is an amount of abrasive particles or a blend
of abrasive particles, weighing less than the maximum weight in
grams that can be applied, that is applied to a make coat of a
coated abrasive article. An open coat abrasive layer will result in
less than 100% coverage of the make coat with abrasive particles
thereby leaving open areas and a visible resin layer between the
particles.
It is believed that if too many of the shaped abrasive particles
with a sloping sidewall are applied to the backing, insufficient
spaces between the particles will be present to allow for them to
lean or tip prior to curing the make and size coats. In various
embodiments of the invention, greater than 50, 60, 70, 80, or 90
percent of the shaped abrasive particles in the coated abrasive
article having an open or closed coat abrasive layer are tipped or
leaning having an orientation angle .beta. of less than 90 degrees.
Precision aperture screens can be used to evenly space the shaped
abrasive particles while still allowing for them to tip or lean at
significantly higher abrasive particle densities in the abrasive
layer that approach or equal closed coat densities.
Without wishing to be bound by theory, it is believed that an
orientation angle .beta. less than 90 degrees results in enhanced
cutting performance of the shaped abrasive particles with a sloping
sidewall. In various embodiments of the invention, the orientation
angle .beta. for at least a majority of the shaped abrasive
particles with a sloping sidewall in an abrasive layer of a coated
abrasive article can be between about 50 degrees to about 85
degrees, or between about 55 degrees to about 85 degrees, or
between about 60 degrees to about 85 degrees, or between about 65
degrees to about 85 degrees, or between about 70 degrees to about
85 degrees, or between about 75 degrees to about 85 degrees, or
between about 80 degrees to about 85 degrees.
The shaped abrasive particles 20 with a sloping sidewall can have
various volumetric aspect ratios. The volumetric aspect ratio is
defined as the ratio of the maximum cross sectional area passing
through the centroid of a volume divided by the minimum cross
sectional area passing through the centroid. For some shapes, the
maximum or minimum cross sectional area may be a plane tipped,
angled, or tilted with respect to the external geometry of the
shape. For example, a sphere would have a volumetric aspect ratio
of 1.000 while a cube will have a volumetric aspect ratio of 1.414.
A shaped abrasive particle in the form of an equilateral triangle
having each side equal to length A and a uniform thickness equal to
A will have a volumetric aspect ratio of 1.54, and if the uniform
thickness is reduced to 0.25 A, the volumetric aspect ratio is
increased to 2.64. It is believed that shaped abrasive particles
having a larger volumetric aspect ratio have enhanced cutting
performance. In various embodiments of the invention, the
volumetric aspect ratio for the shaped abrasive particles with a
sloping sidewall can be greater than about 1.15, or greater than
about 1.50, or greater than about 2.0, or between about 1.15 to
about 10.0, or between about 1.20 to about 5.0, or between about
1.30 to about 3.0.
Other suitable shaped abrasive particles are disclosed in U.S.
patent publication 2009/0169816; U.S. patent publication
2010/0146867; U.S. patent publication 2010/0319269; U.S. patent
application 61/266,000 filed on Dec. 2, 2009 entitled "Dual tapered
Shaped Abrasive Particles"; U.S. patent application 61/328,482
filed on Apr. 27, 2010 entitled "Ceramic Shaped Abrasive Particles,
Method Of Making The Same, And Abrasive Articles Containing The
Same"; and U.S. patent application 61/370,497 filed on Aug. 4, 2010
entitled "Intersecting Plate Shaped Abrasive Particles".
Materials that can be made into formed ceramic abrasive particles
include physical precursors such as finely divided particles of
known ceramic materials such as alpha alumina, silicon carbide,
alumina/zirconia and boron carbide. Also included are chemical
and/or morphological precursors such as aluminum trihydrate,
boehmite, gamma alumina and other transitional aluminas and
bauxite. The most useful of the above are typically based on
alumina and its physical or chemical precursors. It is to be
understood however that the invention is not so limited but is
capable of being adapted for use with a plurality of different
precursor ceramic materials.
Suitable methods for making formed ceramic abrasive particles are
disclosed in: U.S. patent publication 2009/0165394 filed on Dec.
17, 2008 entitled "Method Of Making Abrasive Shards, Shaped
Abrasive Particles With An Opening, Or Dish-shaped Abrasive
Particles"; U.S. patent application Ser. No. 61/289,188 filed on
Dec. 22, 2009 entitled Transfer Assisted Screen Printing Method Of
Making Shaped Abrasive Particles And The Resulting Shaped Abrasive
Particles; and in the patents referenced in the definition of
formed ceramic abrasive particle.
Particles suitable for mixing with the shaped abrasive particles 20
with a sloping sidewall 22 include conventional abrasive grains,
diluent grains, or erodable agglomerates, such as those described
in U.S. Pat. Nos. 4,799,939 and 5,078,753. Representative examples
of conventional abrasive grains include fused aluminum oxide,
silicon carbide, garnet, fused alumina zirconia, cubic boron
nitride, diamond, and the like. Representative examples of diluent
grains include marble, gypsum, and glass. Blends of differently
shaped abrasive particles 20 with a sloping sidewall 22 (triangles
and squares for example) or blends of shaped abrasive particles 20
with different draft angles (for example particles having an 98
degree draft angle mixed with particles having a 120 degree draft
angle) can be used in abrasive articles.
The shaped abrasive particles 20 with a sloping sidewall 22 may
also have a surface coating. Surface coatings are known to improve
the adhesion between abrasive grains and the binder in abrasive
articles or can be used to aid in electrostatic deposition of the
shaped abrasive particles 20. Such surface coatings are described
in U.S. Pat. Nos. 5,213,591; 5,011,508; 1,910,444; 3,041,156;
5,009,675; 5,085,671; 4,997,461; and 5,042,991. Additionally, the
surface coating may prevent the shaped abrasive particle from
capping. Capping is the term to describe the phenomenon where metal
particles from the workpiece being abraded become welded to the
tops of the shaped abrasive particles. Surface coatings to perform
the above functions are known to those of skill in the art.
Coated Abrasive Article Having Z-Direction Rotationally Aligned
Abrasive Particles
Referring to FIG. 1C, a coated abrasive article 40 comprises a
backing 42 having a first layer of binder, hereinafter referred to
as the make coat 44, applied over a first major surface 41 of
backing 42. Attached or partially embedded in the make coat 44 are
a plurality of formed ceramic abrasive particles which, in one
embodiment, comprises shaped abrasive particles 20 with a sloping
sidewall 22 forming an abrasive layer. Over the shaped abrasive
particles 20 with a sloping sidewall 22 is a second layer of
binder, hereinafter referred to as the size coat 46. The purpose of
make coat 44 is to secure shaped abrasive particles 20 with the
sloping sidewall 22 to backing 42 and the purpose of size coat 46
is to reinforce shaped abrasive particles 20 with a sloping
sidewall 22. The majority of the shaped abrasive particles 20 with
a sloping sidewall 22 are oriented such that the tip 48 or vertex
points away from the backing 42 and the shaped abrasive particles
are resting on the sloping sidewall 22 and tipped or leaning as
shown.
Each of the plurality of formed ceramic abrasive particles can have
a specified z-direction rotational orientation about a z-axis
passing through the formed ceramic abrasive particle and through
the backing 42 at a 90 degree angle to the backing as shown in FIG.
1C. The formed abrasive particles are orientated with a surface
feature, such as a substantially planar surface of the first face
24 or the second face 26, rotated into a specified angular position
about the z-axis. The specified z-direction rotational orientation
in the coated abrasive article occurs more frequently than would
occur by a random z-directional rotational orientation of the
surface feature due to electrostatic coating or drop coating of the
formed abrasive particles when forming the abrasive layer. As such,
by controlling the z-direction rotational orientation of a
significantly large number of the formed ceramic abrasive
particles, the cut rate, finish, or both of the coated abrasive
article can be varied from those manufactured using an
electrostatic coating method. In various embodiments of the
invention, at least 50, 51, 55, 60, 65, 70, 75, 80, 85, 90, 95, or
99 percent of the formed ceramic abrasive particles in the abrasive
layer can have a specified z-direction rotational orientation which
does not occur randomly and which can be substantially the same for
all of the aligned particles. In other embodiments, about 50
percent of the formed ceramic abrasive particles can be aligned in
a first direction and about 50 percent of the formed ceramic
abrasive particles can be aligned in a second direction (FIGS. 5A,
5B). In one embodiment, the first direction is substantially
orthogonal to the second direction.
The surface feature is formed during the molding, extrusion, screen
printing or other process that shapes the formed ceramic abrasive
particle. Non-limiting surface features can include: a
substantially planer surface; a substantially planar surface having
a triangular, rectangular, hexagonal, or polygonal perimeter; a
concave surface; a convex surface; a vertex; an aperture; a ridge;
a line or a plurality of lines; a protrusion; or a depression. The
surface feature is often chosen to change the cut rate, reduce wear
of the formed abrasive particles, or change the resulting finish.
Often, the surface feature will be an edge, a plane, or a point and
the z-direction rotational orientation of that feature in the
abrasive layer will be selected taking into consideration the
motion of the abrasive layer, the motion of the work piece, and the
angle of the abrasive layer relative to the workpiece surface
during grinding.
Referring now to FIGS. 2A, 2B through 5A, 5B; various patterns of
the formed ceramic abrasive particles in the abrasive layer of
coated abrasive discs, sheets, or belts are illustrated. The
illustrations represent top views of the abrasive layer having a
plurality of shaped abrasive particles as shown in FIGS. 1A, B. For
simplicity, each individual shaped abrasive particle is represented
as a short line segment representative of the position of the base
(sloping sidewall) of the shaped abrasive particle attached to the
make coat. In the illustrations representative of a sheet or belt,
a longitudinal axis 50 is drawn for reference. Arrows indicating
the disc's or belt's direction of travel when placed onto grinding
tool are additionally provided.
Referring now to FIGS. 2A, 2B, the coated abrasive article can
comprise a disc 52 or a sheet 54 or a belt 54. In FIG. 2A the
coated abrasive article is a disc and the specified z-direction
rotational orientation positions the substantially planar surface
56 circumferentially and the pattern created by the plurality of
formed ceramic abrasive particles comprises a plurality of
concentric circles. In FIG. 2B, the coated abrasive article is a
sheet 54 or a belt 54 and the specified z-direction rotational
orientation positions the substantially planar surface 56 at an
angle of approximately 0 degrees to the longitudinal axis 50 of the
belt or the sheet and the pattern created by the plurality of
formed ceramic abrasive particles comprises a plurality of parallel
lines. Referring to FIG. 2C, the precision apertured screen 58 for
precisely placing and rotationally aligning the formed abrasive
particles when making the disc in FIG. 2A is shown.
Referring now to FIGS. 3A, 3B, the coated abrasive article can
comprise a disc 52 or a sheet 54 or a belt 54. In FIG. 3A the
coated abrasive article is a disc 52 and the specified z-direction
rotational orientation positions the substantially planar surface
56 radically and the pattern created by the plurality of formed
ceramic abrasive particles comprises a plurality of concentric
circles. In FIG. 3B the coated abrasive article comprises a sheet
54 or a belt 54 and the specified z-direction rotational
orientation positions the substantially planar surface 56 at an
angle of approximately 90 degrees to the longitudinal axis 50 of
the belt or the sheet and the pattern created by the plurality of
formed ceramic abrasive particles comprises a plurality of parallel
lines. Referring to FIG. 3C, the precision apertured screen 58 for
precisely placing and rotationally aligning the formed abrasive
particles when making the disc in FIG. 3A is shown.
Referring now to FIGS. 4A, 4B, the coated abrasive article can
comprise a disc 52 or a sheet 54 or a belt 54. In FIG. 4A the
coated abrasive article is a disc 52 and the specified z-direction
rotational orientation positions the substantially planar surface
56 at an angle of approximately 45 degrees to a diameter 60 of the
disc and the pattern created by the plurality of formed ceramic
abrasive particles comprises a plurality of parallel lines. In FIG.
4B the coated abrasive article is a sheet 54 or a belt 54 and the
specified z-direction rotational orientation positions the
substantially planar surface 56 at an angle of approximately 45
degrees to the longitudinal axis 50 of the belt or the sheet and
the pattern created by the plurality of formed ceramic abrasive
particles comprises a plurality of parallel lines. Referring to
FIG. 4C, the precision apertured screen 58 for precisely placing
and rotationally aligning the formed abrasive particles when making
the disc in FIG. 4A is shown. In other embodiments, the
substantially planar surface can be positioned at any angle between
0 degrees and 90 degrees such as 5, 10, 20, 25, 30, 35, 40, 45, 50,
55, 60, 65, 70, 75, 80, and 85 degrees. Ranges of the foregoing
angular rotations are possible by selecting any two of the listed
values to create and an upper and a lower limit.
Referring now to FIGS. 5A, 5B, the coated abrasive article can
comprise a disc 52 or a sheet 54 or a belt 54. In FIG. 5A the
coated abrasive article is a disc 52 and the specified z-direction
rotational orientation positions approximately 50 percent of the
formed abrasive particles having the substantially planar surface
56 aligned at approximately 0 degrees and approximately 50 percent
of the formed abrasive particles having the substantially planar
surface 56 aligned at an angle of approximately 90 degrees and the
pattern created by the plurality of formed ceramic abrasive
particles comprises a plurality of orthogonal lines. In FIG. 5B the
coated abrasive article is a sheet 54 or a belt 54 and the
specified z-direction rotational orientation positions
approximately 50 percent of the formed abrasive particles having
the substantially planar surface 56 aligned at approximately 0
degrees to the longitudinal axis 50 and approximately 50 percent of
the formed abrasive particles having the substantially planar
surface 56 aligned at an angle of approximately 90 degrees to the
longitudinal axis 50 and a pattern created by the plurality of
formed ceramic abrasive particles comprises a plurality of
orthogonal lines. Referring to FIG. 5C, the precision apertured
screen 58 for precisely placing and rotationally aligning the
formed abrasive particles when making the disc in FIG. 5A is
shown.
The make coat 44 and size coat 46 comprise a resinous adhesive. The
resinous adhesive of the make coat 44 can be the same as or
different from that of the size coat 46. Examples of resinous
adhesives that are suitable for these coats include phenolic
resins, epoxy resins, urea-formaldehyde resins, acrylate resins,
aminoplast resins, melamine resins, acrylated epoxy resins,
urethane resins and combinations thereof. In addition to the
resinous adhesive, the make coat 44 or size coat 46, or both coats,
may further comprise additives that are known in the art, such as,
for example, fillers, grinding aids, wetting agents, surfactants,
dyes, pigments, coupling agents, adhesion promoters, and
combinations thereof. Examples of fillers include calcium
carbonate, silica, talc, clay, calcium metasilicate, dolomite,
aluminum sulfate and combinations thereof.
Suitable flexible backings include polymeric films, metal foils,
woven fabrics, knitted fabrics, paper, vulcanized fiber, nonwovens,
foams, screens, laminates, and combinations thereof. The coated
abrasive article with a flexible backing may be in the form of
sheets, discs, belts, pads, or rolls. In some embodiments, the
backing should be sufficiently flexible to allow the coated
abrasive article to be formed into a loop to make an abrasive belt
that can be run on suitable grinding equipment.
A grinding aid can be applied to the coated abrasive article. A
grinding aid is defined as particulate material, the addition of
which has a significant effect on the chemical and physical
processes of abrading, thereby resulting in improved performance.
Grinding aids encompass a wide variety of different materials and
can be inorganic or organic. Examples of chemical groups of
grinding aids include waxes, organic halide compounds, halide
salts, and metals and their alloys. The organic halide compounds
will typically break down during abrading and release a halogen
acid or a gaseous halide compound. Examples of such materials
include chlorinated waxes, such as tetrachloronaphthalene,
pentachloronaphthalene; and polyvinyl chloride. Examples of halide
salts include sodium chloride, potassium cryolite, sodium cryolite,
ammonium cryolite, potassium tetrafluoroborate, sodium
tetrafluoroborate, silicon fluorides, potassium chloride, magnesium
chloride. Examples of metals include tin, lead, bismuth, cobalt,
antimony, cadmium, iron, and titanium. Other grinding aids include
sulfur, organic sulfur compounds, graphite, and metallic sulfides.
It is also within the scope of this invention to use a combination
of different grinding aids; in some instances, this may produce a
synergistic effect. In one embodiment, the grinding aid was
cryolite or potassium tetrafluoroborate. The amount of such
additives can be adjusted to give desired properties.
It is also within the scope of this invention to utilize a
supersize coating over the size coating. The supersize coating
typically contains a binder and a grinding aid. The binders can be
formed from such materials as phenolic resins, acrylate resins,
epoxy resins, urea-formaldehyde resins, melamine resins, urethane
resins, and combinations thereof.
Methods of Making Coated Abrasive Articles Having Z-Direction
Rotationally Aligned Abrasive Particles
Various methods can be used to make the coated abrasive articles of
the present disclosure. In one embodiment, an electrostatic coating
method can be employed as described in copending patent application
having U.S. patent application Ser. No. 61/443,399 filed on Feb.
16, 2011 entitled "Electrostatic Abrasive Particle Coating
Apparatus and Method." In this particular method, an
electrostatically charged vibratory feeder can be used to propel
formed abrasive particles off of a feeding surface towards a
conductive member located behind the coated backing. In some
embodiments, the feeding surface is substantially horizontal and
the coated backing is traveling substantially vertically. It was
surprisingly found that varying the gap between the feeding surface
and the conductive member in contact with the backing changes the
z-direction rotational orientation of formed abrasive particles
comprising thin triangular plates from predominately cross machine
direction aligned plates to predominately machine direction aligned
plates as seen in FIGS. 8 and 9 of the patent application.
Another method of achieving z-direction rotational orientation of
formed abrasive particles can use precision apertured screens that
position the formed abrasive particle into a specific z-direction
rotational orientation such that the formed abrasive particle can
only fit into the precision apertured screen in a few specific
orientations such as less than or equal to 4, 3, 2, or 1
orientations. For example, a rectangular opening just slightly
bigger than the cross section of a formed abrasive particle
comprising a rectangular plate will orient the formed abrasive
particle in one of two possible 180 degree opposed z-direction
rotational orientations. The precision apertured screen can be
designed such that the formed abrasive particles, while positioned
in the screen's apertures, can rotate about their z-axis (normal to
the screen's surface when the formed abrasive particles are
positioned in the aperture) less than or equal to about 30, 20, 10,
5, 2, or 1 angular degrees.
The precision apertured screen having a plurality of apertures
selected to z-directionally orient formed abrasive particles into a
pattern, can have a retaining member such as adhesive tape on a
second precision apertured screen with a matching aperture pattern,
an electrostatic field used to hold the particles in the first
precision screen or a mechanical lock such as two precision
apertured screens with matching aperture patterns twisted in
opposite directions to pinch the particles within the apertures.
The first precision aperture screen is filled with the formed
abrasive particles, and the retaining member is used to hold the
formed abrasive particles in place in the apertures. In one
embodiment, adhesive tape on the surface of a second precision
aperture screen aligned in a stack with the first precision
aperture screen causes the formed abrasive particles to stay in the
apertures of the first precision screen stuck to the surface of the
tape exposed in the second precision aperture screen's
apertures.
A coated backing having a make layer is positioned parallel to the
first precision aperture screen surface containing the plurality of
formed abrasive particles with the make layer facing the formed
abrasive particles in the apertures. Thereafter, the coated backing
and the first precision aperture screen are brought into contact to
adhere the formed abrasive particles to the make layer. The
retaining member is released such as removing the second precision
aperture screen with taped surface, untwisting the two precision
aperture screens, or eliminating the electrostatic field. Then the
first precision aperture screen is then removed leaving the formed
abrasive particles having a specified z-directional rotational
orientation on the coated abrasive article for further conventional
processing such as applying a size coat and curing the make and
size coats.
EXAMPLES
Objects and advantages of this disclosure are further illustrated
by the following non-limiting examples. The particular materials
and amounts thereof recited in these examples as well as other
conditions and details, should not be construed to unduly limit
this disclosure. Unless otherwise noted, all parts, percentages,
ratios, etc. in the Examples and the rest of the specification are
by weight.
Examples 1-4
Shaped abrasive particles were prepared according to the disclosure
of U.S. patent publication 2010/0151196. The shaped abrasive
particles were prepared by molding alumina sol gel in equilateral
triangle-shaped polypropylene mold cavities of side length 0.068
inch (1.73 mm) and a mold depth of 0.012 inch (0.3 mm). After
drying and firing, the resulting shaped abrasive particles
resembled FIG. 1A except the draft angle .alpha. was approximately
98 degrees. The fired shaped abrasive particles were about 0.8 mm
(side length).times.0.2 mm thick and would pass through a 30-mesh
sieve.
Eight inch diameter by 10 mil thick (20.3 cm.times.0.254 mm)
circular precision apertured metal screens were obtained from
Fotofab Inc., Chicago Ill. The precision aperture screens were
produced by photolithographic chemical etching. The individual
apertures were etched from rectangular lithographic features. Due
to the etching process, the actual features had rounded corners and
the apertures were larger on the front and back surfaces than at
the center of the sheet. The maximum surface dimension of each
aperture was approximately 0.39 mm wide by 0.8 mm long. The
dimension at the narrowest portion of each aperture was
approximately 0.34 mm wide by 0.7 mm long.
Four different screen patterns were produced, each having the same
density of apertures. The first screen, FIG. 3C (Example 1), had
concentric rings of apertures where the long dimension of each
aperture was oriented radially with respect to the circular
precision aperture screen. The second screen, FIG. 2C (Example 2),
had concentric rings of apertures where the long dimension of each
aperture was oriented circumferentially with respect to the
circular precision aperture screen. In the third screen, FIG. 4C
(Example 3), the apertures were in concentric rings with the
apertures oriented at an angle halfway between the first two
screens, i.e. with a 45 degree offset from either the radial or the
circumferential orientation. The fourth screen, FIG. 5C (Example
4), was made with apertures on a rectangular array with a repeat
pattern altering vertical and horizontal apertures in each row with
succeeding rows offset relative to each other such that each
horizontal aperture is surrounded by four vertical apertures and
each vertical aperture is surrounded by four horizontal apertures
excepting at the screen's outer circular edge where the pattern may
be cut off.
In order to properly restrain and orient the shaped abrasive
particles in the screen apertures, it was necessary to stack two
precision aperture screens on top of each other with all of the
apertures aligned. The two identical precision aperture screens
were held in alignment and secured with small tabs of foil tape at
the screen's edges. One face of one screen of the indexed screen
stack was then covered with masking tape ("SCOTCH 233+", 53/4 inch
width, 3M Co. St Paul, Minn.). The indexed screen stack was now
ready to receive shaped abrasive particles.
The dimensions of the shaped abrasive particles were such that only
the vertex of a triangular plate would fit into the screen
aperture, and only when it was oriented parallel to the long axis
of the aperture can the vertex of the shaped abrasive particle
contact the adhesive surface of the tape at the bottom of the
aperture on the bottom screen.
A quantity of the shaped abrasive particles was applied to the
surface of the indexed screen stack opposite the tape covered
bottom screen surface and the indexed screen stack was gently
tapped from the bottom. The indexed apertures were soon filled with
shaped abrasive particles held vertex down and base up and oriented
in the direction of the aperture's long dimension. Additional
shaped abrasive particles were applied in this manner until greater
than 90 percent of the apertures contained shaped abrasive
particles that were secured by the exposed masking tape adhesive at
their apexes.
A make resin was prepared by mixing 22.3 parts epoxy resin ("HELOXY
48", Hexion Specialty Chemicals, Houston, Tex.), 6.2 parts acrylate
monomer ("TMPTA", UCB Radcure, Savannah, Ga.) and adding 1.2 parts
photoinitiator ("IRGACURE 651", Ciba Specialty Chemicals,
Hawthorne, N.Y.) with heating until the photoinitiator was
dissolved. 51 parts resole phenolic resin (based-catalyzed
condensate from 1.5:1 to 2.1:1 molar ratio of phenol:formaldehyde),
73 parts calcium carbonate (HUBERCARB, Huber Engineered Materials,
Quincy, Ill.) and 8 parts water were added with mixing. 4.5 grams
of this mixture was then applied via a brush to a 7 in (17.8 cm)
diameter.times.0.83 mm thick vulcanized fiber web ("DYNOS
Vulcanized Fibre", DYNOS GmbH, Troisdorf, Germany) having a 0.875
in (2.22 cm) center hole. The coated abrasive disc was then passed
under a UV lamp at 20 ft/min (6.1 m/min) to gel the coating.
The foil tape tabs connecting the two precision aperture screens
were removed from the shaped abrasive particle filled indexed
screen stack. The shaped abrasive particles themselves in the
apertures were sufficient to index the two screens. The make
resin-coated fiber disc was placed make resin side up on a flat
surface. The shaped abrasive particle filled indexed screen stack
was centered on the fiber disc and the mineral-loaded face was
placed in contact with the make resin. While holding the assembly
stationary, the top precision aperture screen having the taped
surface was carefully separated from the bottom precision aperture
screen containing the shaped abrasive particles, releasing the
shaped abrasive particles. The bottom precision aperture screen was
then carefully lifted from the make resin surface of the fiber
disc. This resulted in the shaped abrasive particles being
transferred to make resin with their vertexes up while largely
maintaining the z-direction rotational orientation established by
the screen's apertures. The weight of the shaped abrasive particles
transferred to each disc was 3.5 grams. The make resin was
thermally cured (90 degrees C. for 90 minutes followed by 105
degrees C. for 3 hours). Each disc was then coated with a
conventional cryolite-containing phenolic size resin and cured (90
degrees C. for 90 minutes followed by 16 hours at 105 degrees
C.).
The finished coated abrasive discs were allowed to equilibrate at
ambient humidity for a week followed by 2 days at 50% RH before
testing.
Comparative Example A
Comparative Example A was prepared identically to Examples 1-4
except that the shaped abrasive particles were applied via
electrostatic coating and were therefore had a random z-direction
rotational orientation.
Grinding Test Method
The grinding performance of the various discs was evaluated by
grinding 1018 mild carbon steel using the following procedure.
Seven inch (17.8 cm) diameter abrasive discs for evaluation were
attached to a rotary grinder fitted with a 7-inch (17.8 cm) smooth
disc pad face plate ("821197 Hard Black" obtained from 3M Company,
St. Paul, Minn.). The grinder was then activated and urged against
an end face of a 0.75.times.0.75 in (1.9.times.1.9 cm) pre-weighed
1018 steel bar under a load of 12 lb (5.4 kg). The resulting
rotational speed of the grinder under this load and against this
workpiece was 5000 rpm. The workpiece was abraded under these
conditions for 10-second grinding intervals (passes). Following
each 10-second interval, the workpiece was allowed to cool to room
temperature and weighed to determine the cut of the abrasive
operation. Test results were reported as the incremental cut for
each interval and the total cut removed. The test end point was
determined when the cut fell below 20% of the initial cut value.
The test was repeated for all Examples at an 8-lb (3.6 kg) load. If
desired, the testing can be automated using suitable equipment.
TABLE-US-00001 TABLE 1 Grinding Results Test load 8 lbs 12 lbs Cut
Comp. Comp. Comp. cycle Example 1 Example 2 Example 3 Ex. A Ex. A
Example 1 Example 2 Example 3 Example 4 Ex A 1 6.86 19.28 15.77
22.34 20.56 6.2 23.45 8.85 26.64 33.63 2 3.22 23.3 9.1 17.45 23.29
1.7 7.87 4.03 6.84 26.51 3 2.27 19.64 7.62 11.29 18.6 1.14 4.94
3.05 4.09 10.08 4 2.05 13.39 5.55 7.72 11.39 3.92 2.38 6.12 5 1.82
9.1 4.5 6.81 8.24 2.1 6 1.63 6.58 4.06 5.79 6.43 1.97 7 1.35 6.18
3.62 5.36 5.23 1.71 8 5.81 3.52 4.55 4.58 9 5.34 3.41 3.94 4.15 10
5.02 3.3 3.88 11 4.32 2.99 12 3.9 13 3.77 Total 19.2 125.63 63.44
85.25 106.35 9.04 40.18 24.09 37.57 76.34
Test results are shown in Table 1. FIG. 6 plots the cut results for
various Example disks and the e-coated Control disc under a 12 lb
load and FIG. 7 plots the cut results for various Example disks and
the e-coated Control discs under the 8 pound load. As seen, varying
the z-direction rotational orientation of the substantially planar
surface significantly affected the cut rate of the various Example
discs.
Example 5
In Example 5, apertured screens were used to control the vertex up
orientation of triangular shaped abrasive particles in screen
coated abrasive discs and compared to electrostatically coated
(e-coated) Control abrasive discs for total cut on stainless steel.
The weight of the triangular shaped abrasive particles placed into
the apertured screen was varied and compared to e-coated control
discs of the triangular shaped abrasive particles of various
weights. In this example a simple 28 mesh woven wire sieve screen
was used to align the triangular shaped abrasive particles in the
proper vertex up orientation. The triangular shaped particles were
prepared by shaping alumina sol gel from equilateral,
triangular-shaped polypropylene mold cavities of side length 110
mils, a mold depth of 28 mils, and a 98 degree draft angle. After
drying and firing, the resulting triangular shaped abrasive
particles had a side length of about 0.110'' (2.8 mm), a thickness
of about 0.012'' (0.3 mm), and a -20+26 mesh sieve size.
For these screen coated abrasive discs, the rotational alignment of
the triangular shaped abrasive particles was not controlled, and
the screen's apertures allowed for a random z-direction rotational
orientation. However, the apertured screens assured that
approximately 100 percent of the triangular shaped abrasive grain
in the abrasive layer had its vertex pointing away from the
backing. As the percent closed coat density is increased for the
e-coated samples, more and more of the triangular shaped abrasive
particles become attached in the abrasive layer by their vertex
thereby presenting a horizontal surface to the workpiece to be
abraded. As seen in FIG. 8, the screen coated discs had
significantly higher cut at percent closed coat densities greater
than 75 percent. In various embodiments of the invention, screen
coated discs can have a percent closed coat density from about 75
to about 100 percent, or from about 80 to about 98 percent. At
these densities, significantly more shaped abrasive particles
comprising triangular plates are attached to the make layer by the
triangle's base with the vertex pointing away from the make layer
significantly enhancing the total cut of the coated abrasive
article.
Other modifications and variations to the present disclosure may be
practiced by those of ordinary skill in the art, without departing
from the spirit and scope of the present disclosure, which is more
particularly set forth in the appended claims. It is understood
that aspects of the various embodiments may be interchanged in
whole or part or combined with other aspects of the various
embodiments. All cited references, patents, or patent applications
in the above application for letters patent are herein incorporated
by reference in their entirety in a consistent manner. In the event
of inconsistencies or contradictions between portions of the
incorporated references and this application, the information in
the preceding description shall control. The preceding description,
given in order to enable one of ordinary skill in the art to
practice the claimed disclosure, is not to be construed as limiting
the scope of the disclosure, which is defined by the claims and all
equivalents thereto.
* * * * *